Antennas are used in a variety of devices to transmit electrical currents, converted into radio waves, to a remote device that also has an antenna. Antennas come in many types, but each one has a metallic surface for radiating and receiving the electromagnetic energy. Recently, antennas are even being embedded into printed circuit boards.
Typically, antennas are designed to send and receive signals within a particular range of frequencies. An antenna designed for broadband use may not necessarily be suited to a narrowband device. Despite this limitation, some antennas may be adjusted to operate under different applications.
A simplified system 100 with a prior art antenna 44 is depicted in FIG. 1. The antenna 44 is connected to a transceiver 40, which converts electrical signals to radio waves, making them suitable for transmission over air. Likewise, the transceiver converts received radio waves into electrical signals. The antenna 44 is also connected to a varactor 46 and a waveform generator 42.
The waveform generator 42 drives the varactor 46 (a variable capacitor), which adjusts the properties of the antenna 44 so as to change the resonant frequencies and the antenna bandwidth in which the antenna operates. This makes the antenna 44 more flexible in its operation, but the waveform generator 42 and varactor 46 also increase the cost, size, and complexity of the system 100. In addition to this, an off-the-shelf variable capacitor is a non-linear device, which has the potential to generate undesired intermodulation in the transceiver 40.
Thus, there is a continuing need for a time-variant antenna that overcomes the shortcomings of the prior art.